The Session Initiation Protocol (SIP) is a signaling protocol that provides a mechanism for a computing device to locate another device it wants to communicate with over a computer network and to establish a communication session therewith. In particular, SIP is an Internet Engineering Task Force (IETF) standard protocol for initiating interactive user-sessions in a number of scenarios. For example, SIP is used for Internet conferencing, telephony, gaming, virtual reality, event notification, and instant messaging. The SIP protocol enables call setup initiation, routing, authentication and other feature messages to endpoints within an IP domain.
Like HTTP or SMTP, SIP works in the Application Layer of the Open Systems Interconnection (OSI) communications model. As such, SIP can establish multimedia sessions or Internet telephony calls, and modify or terminate them. The SIP protocol can also invite participants to unicast or multicast sessions that do not necessarily involve the initiator. Because the SIP supports name mapping and redirection services, users initiate and receive communications and services from any location and networks are capable of identifying users within the network.
Although SIP has been widely implemented for various applications, the current SIP protocol has a deficiency whereby there is no unique identifier for a device carried in the SIP signal. The standard SIP solution is to use the device's IP address, however, this is not an adequate solution because in many situations the device itself remains the same yet the device's IP address changes, as in the case of a reboot.
As such, it is desirable to identify endpoint devices which are involved in a security association (SA) (i.e., a point to point association which is not shared across multiple devices for a user). In particular, tying the SA to the IP-level communication address means the SA is lost when the communication address changes dynamically. Having a unique identifier would make it possible to re-use an existing SA for situations where the device and user credentials have not changed.
It is also desirable to support independent send and receive communication addresses as in the case of using TCP as a transport wherein it is typical to use different send and receive ports. Because of the difference in the ports, the combination of IP address and port is not suitable for uniquely identifying the device and a single device would be perceived as having two different identities. Using the IP address alone precludes the ability to have two different SIP stacks on the same node. As such, having a unique device identifier would enable independent send and receive communication addresses.
It is further desirable to distinguish between multiple and single point of presence for a user as in the case where a registrar/presence agent server chooses to enforce policies that restrict a user to having only a single point of presence. In such a situation, a unique device identifier would be beneficial in allowing the registrar to distinguish when a user has registered multiple clients versus when a user has registered the same client multiple times with a different communication address.
It is still further desirable to allow routing of a request to one of several devices belonging to a particular user. In particular, it is desirable to allow the originator of the request to target a specific destination device and to allow a device to specify that future communications within a dialog should go directly to that device even in situations where the communication address for that device changes over time.
It is yet further desirable to support reliable communications over potentially transient HTTPS connections. Because a unique device identifier is useful for identifying peers in a TLS connection, the remote end of this connection can use the device identifier to determine the appropriate connection to use when forwarding messages, even when the connection is broken and re-established. Similarly, it is desirable to use the unique device identifier to manage a reboot/restart of a client such that changes in the communication address are differentiated from changes in the device.
Thus, there is a need to extend the SIP signaling protocol for the purpose of adding an identifier for use in uniquely identifying the end-point device to overcome these and other obstacles.